1. Field of the Invention
The present invention relates to the inhibition and prevention of pitting and corrosion in cooling systems, particularly the pitting and corrosion of "wet" cylinder block sleeves or liners of internal combustion engines. More particularly, the invention provides a coating of a mechanical nature formed over portions of such liners which are normally in contact with corrosive coolant liquids normally found in circulating cooling systems employed in the removal of waste heat from diesel and other internal combustion engines, the coating being preferably formed from a polymerized polyester resin. The present invention provides protection against pitting due to cavitation-erosion, corrosion, and scale formation without the use of chromate, dichromate, inorganic condensed phosphate and organic corrosion inhibitors which are commonly added to coolant liquids.
2. Description of the Prior Art
Internal combustion engines and other apparatus which produce waste heat as a result of operation typically utilize cooling systems which circulate a liquid coolant in contact with portions of the engine or apparatus, heat exchange occurring between said portions and the liquid coolant. The liquid coolant in such systems usually comprises water, often in combination with a second coolant, such as ethylene glycol in amounts up to 15%. In internal combustion engines, particularly diesel engines, having "wet" cylinder blocks, a sleeve or liner separates the cylinder block from the liquid coolant. Typically, oil used in the operation of the engine is disposed on one side of the liner, the opposite side of the liner being in continuous contact with the liquid coolant, heat exchange occurring through the liner between the oil and the liquid coolant. It is well known that coolants, especially water, act to corrode such liners regardless of the metal from which the liner is fabricated. Pitting of such liners also occurs due to cavitation-erosion and other factors, the pitting finally resulting, if the linear is not replaced periodically, in the formation of pinholes which extend through the liner, the coolant liquid then contaminating the lubricant oil on the other side of the liner. An engine can be thereby caused to "seize" or be substantially damaged due to the resulting lack of proper lubrication. At best, the pitter liner must be replaced at substantial cost prior to a normally expected engine over-haul. Corrosion, scale, and other deposits further damage such liners and act to reduce the rate of heat transfer through the liner to the coolant liquid.
Since the above-noted problem is one of long standing in the art, a substantial amount of effort has been directed to a solution thereof. Primarily, the problem has been addressed in the prior art by the provision of chemical additives, such as chromates or dichromates which are dissolved in the coolant liquid, the substance frequency being employed in combination with inorganic condensed phosphates. Such substances are toxic and thereby cause environmental degradation when discharged after use. Certain additives act to form a substantially fluent, nonrigid film on the surfaces of the metallic liners in an effort to resist pitting and corrosion thereof. Since one of the mechanisms by which pitting occurs involves a mechanical bursting of air bubbles against the metal surface, such fluent films and coolant additives are not effective in the prevention of pitting of the surfaces of the liner in contact with the coolant liquid. Attempts have also been made to inhibit the corrosion of metallic surfaces by the formation of a protective metal oxide film. However, soluble species in the film act to migrate from the surface of the metal and are of no appreciable value to ionic and/or molecular corrodants or corrosion products, especially after a relatively short period of time. Degradation of such a metal oxide film results in a rapid corrosion rate due to the fact that dissolved oxygen in the aqueous environment which then contacts the metal surface diffuses to the free metal surface.
Mechanical filters have also been employed which have chemical substances disposed therein, the chemicals being intended to protect surfaces contacting the liquid from corrosion. However, the chemical substances in typical filters go into solution within 30 minutes, of installation of said filter within the cooling system. As with chemical additives of the type described above, loss of the coolant liquid due to boil-over or accidental drainage results in the complete loss of protection against corrosion and cavitation-erosion. Further, a filter in and of itself provides no protection against pitting of the cylinder block liner.
Given the present state of the art, it is obvious that improved protection against pitting and corrosion not only in "wet" sleeve internal combustion engines but also in apparatus having heat exchange surfaces in contact with a circulating liquid is needed.